Lec. 1 Biology PDF

The Science of Biology Biology is a branch of science that deals with living organisms and their vital processes. Why study biology is importance? As a field of science, biology helps us to: 1- Understand the living world and the ways it’s many species (including...

The Science of Biology Biology is a branch of science that deals with living organisms and their vital processes. Why study biology is importance? As a field of science, biology helps us to: 1- Understand the living world and the ways it’s many species (including humans) function, evolve, and interact. 2- Advances in medicine, agriculture, biotechnology, and many other areas of biology have brought improvements in the quality of life. 3- Fields such as genetics and evolution give insight into the past and can help shape the future, 4- Research in ecology and conservation inform how we can protect this planet’s precious biodiversity. Some subdivision of biology Biology is subdivided into separate branches for convenience of study, though all the subdivisions are interrelated by basic principles. Thus, 1- while it is custom to separate the study of plants (botany) from that of animals (zoology) 2- and the study of the structure of organisms (morphology) from that of function (physiology), all living things share in common certain biological phenomena—for example, various means of reproduction, cell division, and the transmission of genetic material. 3- Molecular biology is the branch of biology that concerns the molecular basis of biological activity in and between cells, including molecular synthesis, modification, mechanisms and I  interactions. The molecular biology describes the process in which DNA is transcribed into RNA, and then translated into protein. 4- Those broadly based levels—molecules, cells, whole organisms, and populations—may be further subdivided for study, giving rise to specializations such as: morphology, taxonomy, biophysics, biochemistry, genetics, epigenetics, and ecology. 5- A field of biology may be especially concerned with the investigation of one kind of living thing—for example, the study of birds in ornithology, the study of fishes in ichthyology, or the study of microorganisms in microbiology. Basic Concepts of Biology Characteristic of living organism 1- Movement. All living things move in some way. 2- Respiration. Respiration is a chemical reaction that happens within cells to release energy from food. 3- Sensitivity. The ability to detect changes in the surrounding environment. 4- Growth. 5- Reproduction. 6- Excretion. 7- Nutrition. 8- Evolution 9- Adaptation 10- Homeostasis 11- Metabolism ( anabolism & catabolism) Biological principles 1-Homeostasis the tendency of biological systems to maintain relatively constant conditions in t II he internal envirnment while continuously interacting with and adjusting to changes origin ating within or outside the system. Any self-regulating process by which biological systems tend to maintain stability while adjusting to conditions, that are optimal for survival. If homeostasis is successful, life continues; if unsuccessful, disaster or death ensues. The stability attained is actually a dynamic equilibrium, in which continuous change occurs yet relatively uniform conditions prevail. 2- Unity All living organisms, have certain biological, chemical, and physical characteristics in common. All, for example, are composed of basic units known as cells and of the same chemical substances, which, when analyzed, exhibit noteworthy similarities, even in such disparate organisms as bacteria and humans. There is not only unity of basic living substance and functioning but also unity of origin of all living things. According to a theory proposed in 1855 by German pathologist Rudolf Virchow “all living cells arise from pre-existing living cells.” That theory appears to be true for all living things at the present time under existing environmental conditions. III Animal cells and plant cells contain membrane-bound organelles, including a distinct nucleus. In contrast, bacterial cells do not contain organelles. 3- Metabolism The word metabolism can also refer to the sum of all chemical reactions that occur in living organisms, including digestion and the transport of substances into and between different cells, in which case the above described set of reactions within the cells is called intermediary metabolism or intermediate metabolism). Metabolic reactions may be categorized as: a- catabolic - the breaking down of compounds (for example, the breaking down of glucose to pyruvate by cellular respiration); or b- anabolic - the building up (synthesis) of compounds (such as proteins, carbohydrates, lipids, and nucleic acids). Usually, catabolism releases energy, and anabolism consumes energy. IV  Metabolism Is the set of life-sustaining chemical reactions in organisms. The three main purposes of metabolism are: 1-the conversion of food to energy to run cellular processes; 2-the conversion of food/fuel to building blocks for proteins, lipids, nucleic acids, and some carbohydrates; 3- the elimination of nitrogenous wastes. These enzyme-catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments. The chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed through a series of steps into another chemical, each step being facilitated by a specific enzyme. Enzymes are important to metabolism because: 1- They allow organisms to drive desirable reactions that require energy that will not occur by themselves, by coupling them to spontaneous reactions that release energy. 2- Enzymes act as catalysts - they allow a reaction to proceed more rapidly – 3- They also allow the regulation of the rate of a metabolic reaction, for example in response to changes in the cell's environment or to signals from other cells. 4- Evolution In his theory of natural selection. Charles Darwin suggested that “survival of the fittest” was the basis for organic evolution (the change of living things with time). Evolution itself is a biological phenomenon common to all living things, even though it has led to their differences. Evidence to support the theory of evolution has come primarily from the fossil record, from comparative studies of structure and function, from studies of embryological development, and from studies of DNA and RNA (ribonucleic acid). V Three types of natural selection, showing the effects of each on the distribution of phenotypes within a population. The downward arrows point to those phenotypes against which selection acts. 1- Stabilizing selection acts against phenotypes at both extremes of the distribution, favouring the multiplication of intermediate phenotypes. 2- Directional selection acts against only one extreme of phenotypes, causing a shift in distribution toward the other extreme. 3- Disruptive diversity (Diversifying selection) acts against intermediate phenotypes, creating a split in distribution toward each extreme. 5- Diversity Despite the basic biological, chemical, and physical similarities found in all living things, a diversity of life exists not only among and between species but also within every natural population. The phenomenon of diversity has had a long history of study VI because so many of the variations that exist in nature are visible to the eye. The fact that organisms changed during prehistoric times and that new variations are constantly evolving can be verified by paleontological records as well as by breeding experiments in the laboratory. Long after Darwin assumed that variations existed; biologists discovered that they are caused by a change in the genetic material (DNA). 1- That change can be a slight alteration in the sequence of the constituents of DNA (nucleotides), 2- larger change such as a structural alteration of a chromosome, 3- A complete change in the number of chromosomes. Taxonomy has been based on two major assumptions: 1-one is that similar body construction can be used as a criterion for a classification grouping. 2- the other is that, in addition to structural similarities, evolutionary and molecular relationships between organisms can be used as a means for determining classification. 6- Behaviour and interrelationships The study of the relationships of living things to each other and to their environment is known as Ecology. Because these interrelationships are so important to the welfare of Earth and because they can be seriously disrupted by human activities, ecology has become an important branch of biology. 7- Continuity Whether an organism is a human or a bacterium, its ability to reproduce is one of the most important characteristics of life. Because life comes only from preexisting life, it is only through reproduction that successive generations can carry on the properties of a species. VII